How many proscar tablets should I add in a 60 ml of Minoxidil bottle to make a 0.1% topical Finasteride?

Oh, it's not so simple. Adding finasteride to this solution does not guarantee it gets into the scalp. That's the challenge and complexity of topical finasteride. Most topical finasteride solutions add some type of lipid - soy phosphatidyl choline or liposomes.  One can not simply add finasteride pills to minoxidil solutions. 

when using any kind of prescription medication, it has to be under the supervision of a medical doctor. You meed to see a hair loss specialist to get the proper care and treatment. 

Finasteride tambles when dissolved in any solution will not be absorbed through the skin to be effective